# 函数None的应用
# 返回值默认返回None
def say_hi():
    print("你好")
say = say_hi()
print(say)

def say_hello():
    print("你好呀")
    return None
say1 = say_hello() 
print(say1)

def say_yes():
    print("nimenhao1")
say_yes()